1. Field of Invention
The invention relates to a disk brake rotor with a wear indicator that does not adversely affect operation of the rotor yet allows easy visual inspection of wear.
2. Description of Related Art
Conventional disk brake rotors generally include a pair of mutually spaced-apart annular disks that form two opposed planar brake contact surfaces. These opposed brake contact surfaces receive braking force as applied by a brake caliper through two opposed brake pads. These rotors encounter frictional forces and heat build up each and every time the brakes are applied. Over time, these rotors (as well as the pads) wear or are damaged due to heat degradation and material fatigue caused by the cyclical application of frictional brake forces. Eventually, both the brake pads and the brake rotors become worn to a point where replacement is warranted or necessary. The full life expectancy of these brake pads and rotors cannot be determined with precision in advance as it is dependent upon many variables. In view of this, most vehicle manufacturers and brake component manufacturing companies recommend periodic inspection of brake components.
For inspection or indication purposes, brake pads routinely include metal wear indicators located to one side of the brake pad. These indicators extend along a thickness of the brake pad by a distance corresponding to a predetermined minimum wear depth. Even if the brake pads are not completely worn out, visual inspection of the brake pads can be easily performed by viewing these indicators and ascertaining whether the pads are worn sufficiently to warrant replacement. Moreover, such brake pads often exhibit an audible sound when the brakes are sufficiently worn to a point where the metal indicators contact the rotor surface during braking. More complex indicators on some vehicles activate circuits that illuminate a warning indicator when brake pads on a vehicle are worn beyond acceptable tolerances. As such, visual or audible indication of brake pad life can be rather easily determined.
The wear on brake rotors is not as readily ascertainable. Visual wear of a brake rotor is hard to ascertain. Each brake rotor is designed for a particular application and has a minimum dimensional thickness after which time the brake rotor no longer operates as desired and is susceptible to unacceptable, and perhaps even dangerous warpage, cracking or reduced braking capability. Some rotors are single use rotors, designed with relatively thin rotor surfaces. Upon sufficient wear, these rotors are intended to be replaced. Other rotors are designed with sufficient rotor thickness such that, after extended use, they can be machined or xe2x80x9cturnedxe2x80x9d one or more times by known conventional equipment back to a smooth, flat surface to eliminate uneven wear patterns, and continue in use. This remachining of the brake contact surfaces of these rotors can be repeated until the rotor has reached a design minimum rotor thickness. As brake rotors often last much longer than the average brake pads, most people servicing brake systems visually inspect the brake pads only and do not measure the wear on the rotors until the pads require replacement.
While a rotor with a severely warped, pitted or scored contact surface may be quickly identified by a trained mechanic""s eye, the remaining life of most rotors, without serious defects, cannot be so readily determnined visually. This is because the remaining life cannot be determined from a cursory review of the contact surfaces, which if the rotors are used properly, will wear down uniformly. Moreover, as different rotors have differing dimensions and minimal thickness design criteria, conventional inspection techniques have typically involved precise measurements of the rotor contact surfaces using a micrometer for both rotor thickness and rotor runout (determination of an out-of-round condition). The resultant readings determine whether the rotor: 1) needs replacement, 2) is within acceptable tolerances, or 3) has sufficient remaining thickness to be machined back to a smooth brake surface.
Such rotor inspections require expensive and properly calibrated equipment. Moreover, such inspections require knowledge of the appropriate minimum rotor thickness for a particular rotor, which is primarily determined by the rotor manufacturer. This information is often stamped on non-contact surfaces of the rotor or may be published in appropriate literature. However, such literature may be unavailable to a typical vehicle owner. Moreover, even stamped tolerances are often difficult to determnine. This is because by the time that sufficient time and braking cycles and wear have occurred to warrant inspection, rust and environmental exposure may have obscured such markings beyond recognition. Further, even upon ascertaining the proper minimum tolerance information, prior inspection techniques required precise micrometer measurements, which cannot be performed by many persons who service vehicles. As such, rapid and accurate inspection of rotors has not been attainable with conventional rotor technology.
Thus, there is a need for a brake rotor that is capable of visual inspection to determine remaining useful life or uneven wear.
The invention overcomes the problems with the prior art by providing a visual indicator of rotor condition without the need for measurement tools.
These and other objects of the invention are overcome by a brake rotor for a vehicle brake system having a visual wear indicator, comprising: a central hub rotatably mountable to a vehicle for rotation about an axis; and at least one radially extending annular disk extending radially from the central hub, the at least one annular disk including inboard and outboard planar brake contact surfaces, the inboard and outboard brake contact surfaces being of a predetermined surface roughness, wherein at least one visual wear indicator is formed on at least one of said inboard and outboard brake contact surfaces solely within a brake contact region of the brake contact surfaces that will be worn due to brake pad contact during use, the visual wear indicator including a recessed surface substantially parallel to the brake contact surface that is at a depth corresponding to a minimum useable thickness of the rotor.
These and other objects are also achieved by a method of forming a visual wear indicator on a brake rotor, comprising the steps of: forming a brake rotor with a central hub rotatably mountable to a vehicle and at least one radially extending annular disk extending radially from the central hub, the at least one annular disk including inboard and outboard planar brake contact surfaces rotatable about an axis of rotation; forming at least one visual wear indicator on at least one of said inboard and outboard brake contact surfaces solely within a brake contact region of the brake contact surfaces that will be worn due to brake pad contact during use, the visual wear indicator including recessed surface substantially parallel to the brake contact surface that is at a depth corresponding to a minimum useable thickness of the rotor; and processing the inboard and outboard brake contact surfaces to have a predetermined surface roughness.
It is believed that for best retention of braking benefits, a visual wear indicator system is needed that is not obtrusive. That is, the wear indicator should not remove much rotor material, so as to maximize rotor mass and surface area. Moreover, the visual wear indicator needs to be provided on a contact surface of the rotor that is contacted by the brake pad so as to be an accurate reflection of rotor surface wear.
The inventive visual wear indicator in a first embodiment of the invention takes the form of a simple counterbore formed on an exterior contact surface of the rotor intermediate radial extremities of the contact surface. Such a location is selected so as to be within an area that is contacted by a brake pad. There may be a counterbore provided diametrically opposite the first bore. This may assist in rotor balancing, but may be unnecessary if the amount of material removed is minimal. The counterbores are preferably formed on opposite surfaces (i.e., one on the outboard rotor surface and one on the inboard rotor surface), but may be formed on the same side. If provided on the same side, they should be provided on both the outboard and inboard rotor surfaces so that both surfaces can be visually checked for wear.
The inventive visual wear indicator in a second embodiment of the invention takes the form of an annular groove provided in the rotor contact surface. Such an annular groove is preferably formed on both the inboard and outboard rotor surfaces so that both surfaces can be inspected for wear.
Alternative exemplary embodiments are also provided and described.